The present invention is concerned with an arrangement for detecting and evaluating of yawing movements of an automotive vehicle which serve as an input quantity of an automatic control system, comprising one or more yaw rate sensors and electronic circuits for processing and evaluating the information obtained by the yaw rate sensors and representing the yawing movements of the automotive vehicle, and for generating control signals.
Measuring and evaluating of yawing movements, namely of angular motions and yawing speeds about the vertical axis of an automotive vehicle, are particularly important in connection with automotive control systems which applies especially to the so-called driving stability control (FRS or ASMS, i.e. automatic stability management system).
Systems for automotive vehicles for controlling and limiting undesired yawing movements about the vertical axis of a vehicle are already known in the art. Intensive development work is designed to improve such systems and to cut manufacturing costs thereof.
In systems of the afore-described type, basically, steering angle, gas pedal position, brake pressure and motion pattern of the vehicle wheels are detected with the aid of sensors, with the nominal yawing movement of the automatic vehicle being computed from such data. At the same time, the transverse acceleration acting upon the automotive vehicle, and the yawing speed are measured. The actual state of yaw of the automotive vehicle is determined from the arithmetic combination of these qualities. If a non-permissive deviation of the actual movement from the nominal movement is detected or imminent, the control is activated, limiting the yawing movement by a controlled actuation of the brake to permissive values not affecting the driving stability.
Driving stability control systems of the afore-described type are required to work with a high precision and reliability in order that the standard and proper driving behavior of the automotive vehicle be maintained, preventing an early activation of the control system affecting the driving comfort or even causing a danger or irritation to the driver.
To that effect, a precise, reliable and error-free determination of the rate of yaw is required. Error-free measured values of the rate of yaw must be detected before the control is affected. It is difficult to measure the yawing movement and to monitor the measuring systems because no defined vehicle motions can be generated in reference to which the yaw rate sensors and the associated evaluating circuits could be checked or calibrated. It is only during standstill of the vehicle that deviations from the zero point can be rectified.
State-of-the-art driving stability control systems employ a single relatively high-precision yaw rate sensor. However, this conception involves the disadvantage that after calibration of the sensor, during standstill of the automotive vehicle, it is no longer possible to directly identify a slowly progressing measured deviation. Such "creeping" inaccuracies can occur as a result of defects of special sensor components or of the evaluating circuits, i.e. as a result of defective condensers, open, high-ohmic semi-conductor inputs, tottering contacts etc.
Errors of this type can only be identified via circumferential factors obtained from auxiliary data or through logical operation that are only indirectly related to the yawing movement. The identifying mechanism responds by a relatively poor resolution and by a higher inertia or delay than in direct reference processes.
To compensate these disadvantages, it will be necessary to detect, in practice, correspondingly more accurate measured values, requiring, in turn, employment of high-precision yaw rate sensors able to provide both a large measuring range and a high dissolution and precision in the small-to-average yaw rates ranges. However, this involves an out-of-proportion relationship between technical efforts and achievable accuracy.
Despite high efforts involved, detection of each and every malfunction of the sensor cannot be safeguarded so that, for safety reasons, the control system will have already to be cut off if temporary circumstances occur arousing the suspicion of malfunction of the system. If such an error or suspected defect occurs during a control operation, the behavior of the system is indefinite. To reduce the malfunction probability to a reasonable degree, maximum requirements must be placed upon the reliability of the components and upon the automatic test function of the sensing system and of the appertaining circuits. Such requirements can, of course, only be complied with by accepting high manufacturing efforts.
It is, therefore, the object of the invention to overcome the afore-described disadvantages involved with conventional systems and sensors and to provide an arrangement of the afore-described type enabling accurate and safe detection of the yawing movement of an automotive vehicle, keeping the efforts and expenses involved low compared to conventional systems, and insuring a quick and safe error detection.